I'm getting this exception:

ERROR [MailActivation] Failed to execute folder check, spec=MailActivationSpec(mailServer=10.0.*.*, storeProtocol=imap, mailFolder=INBOX, pollingInterval=60000, messageSelector=null, userName=*, maxMessages=1)
javax.mail.NoSuchProviderException: Invalid protocol: null
 at javax.mail.Session.getProvider(Session.java:412)
 at javax.mail.Session.getStore(Session.java:511)
 at javax.mail.Session.getStore(Session.java:491)
 at javax.mail.Session.getStore(Session.java:477)
 at org.jboss.resource.adapter.mail.inflow.MailFolder.open(MailFolder.java:69)
 at org.jboss.resource.adapter.mail.inflow.MailActivation.run(MailActivation.java:121)
 at org.jboss.resource.work.WorkWrapper.execute(WorkWrapper.java:204)
 at org.jboss.util.threadpool.BasicTaskWrapper.run(BasicTaskWrapper.java:275)
 at EDU.oswego.cs.dl.util.concurrent.PooledExecutor$Worker.run(PooledExecutor.java:743)
 at java.lang.Thread.run(Thread.java:595)

when jboss tries to get mail for transferring to my mdb. It happans occasionally. I can't find any pattern yet.

Any ideas?

P.S. MailActivation.java is hacked to pint out exception code.